A late 19th century American precursor to the modern day peak flow meter and spirometer. Blowing through this antique spirometry device spins the blades causing the disk to rotate behind a fixed pointer.
The resulting crude assessment of lung function depends on both peak flow and lung capacity. See “Measured Breath” and a picture of this instrument from the Smithsonian Institution. Quackery was never far behind, and it was also considered of benefit to “any lady who desires to symmetrically enlarge her bust”.
- From the Phisick collection